1. Field of the Invention
The present invention relates to a printer of the type in which a heat fusible ink on a transfer material is melted by a thermal head and the melted ink is transferred onto a printing paper to effect printing.
2. Description of the Prior Art
For the conventional serial type thermal printing system, the problem of adhesion between the thermal head and the heat sensitive paper has already been solved due to a great effort made over a long time. Presently available in this type of thermal printer, the thermal head can be returned to the print starting position without any trouble immediately after the end of printing.
However, the case is different for the transfer type thermal printing system in which no heat sensitive paper is used and instead a transfer material such as transfer tape is interposed between a common paper and a thermal head to effect printing on the common paper by the thermal head through the transfer tape. In the case of this thermal transfer printing system, the problem of adhesion between the transfer tape and the printing paper has not yet been solved. In the printer, the transfer tape remains stuck on the recording paper even after the end of printing.
In order to separate the stuck transfer tape from the paper by pulling the tape in the direction in which the thermal head is moved, namely in the direction normal to the adhesion, a large amount of force will be required. In addition, in view of means for holding the recording paper in the position, such pulling force in the direction normal to the adhesion should be avoided. Therefore, separation must be done by pulling the tape in the direction of adhesion. Furthermore, the area of stuck portion must be reduced as much as possible. It may be considered to use a particular power source for mechanically separating such stuck transfer tape from the paper. However, this solution makes the mechanism of the printer complicated and no stable operation can be expected. This problem of adhesion, therefore, constitutes the most important drawback of the known thermal transfer printing system. For better understanding of the subject of the present invention, some further description of the above problem will be made hereinafter with reference to FIGS. 1 through 3.
FIG. 1 schematically shows the structure of an ink ribbon generally used in the thermal transfer printing system. The ink ribbon comprises a base member 1 which may be a film of polyester and an ink layer coated on the base member. The ink layer contains pigment or dye 2 such as carbon black dispersed in a heat fusible binder 3.
FIGS. 2 and 3 illustrate the manner of printing through the ink ribbon. A thermal head 4 is brought into contact with the ink ribbon on the side of its base member 1. An electric current is applied to a heating resistor 5 provided on the thermal head 4 to heat the ink ribbon. A portion of the binder 3 heated by the heating resistor 5 is selectively melted, and the fused portion is transferred onto a printing paper 6. In this manner, printing is performed.
To prevent hands or printing paper from being made dirty by the ink ribbon when contacted, the binder 3 must be coated on the base member 1 with some degree of adhesion. The binder usually has a high degree of affinity to common papers. Therefore, in the phase immediately after thermal transferring as shown in FIG. 2, the ink ribbon and the printing paper 6 are stuck together. At the next step, the printing paper 6 has to be stripped from the ink ribbon with only the printed portion 3a being adhered to the printing paper as shown in FIG. 3.
In the thermal transfer printing apparatus, the stripping step may be carried out after the end of printing one line of characters or several words and during the time in which the next printing is being carried out. However, there may occur a case where the ink ribbon is used up in the middle of printing. In this case, the ink ribbon must be exchanged for a new one while the old ink ribbon is still stuck on the printing paper. To exchange ink ribbons in this state the stuck ink ribbon must be stripped from the printing paper by hand. This is not only time consuming but also damaging. The printing paper 6 may be made dirty or broken and parts of the thermal head 4 also may be damaged during stripping by hand. This is the greatest disadvantage involved in the known thermal printer.